Valves are generally disposed in the course of passages of gas or a liquid for adjusting the flow rate thereof or controlling the opening and closing of the passages. There are instances where a disaster such as an earthquake or a fire may provoke an unforseen severe accident due to leak of combustible gas unless the gas passages are immediately closed. In such case, it is required to emergently close the valves simultaneously with the occurrence of a disaster. However, it is not actually possible to manually operate a plurality of valves simultaneously, specially in a state of disorder at the time of the occurrence of a disaster. Some measures to be taken have therefore been required.
In this connection, there has been proposed an actuator adapted to automatically close a valve by switching an electromagnetic clutch, using the retaining strength of a power spring which has been manually wound in advance. In such actuator, the power spring has to be manually wound in advance, taking much labor, and there is a risk of failure to wind the power spring. Further, the use of expensive electromagnetic clutch disadvantageously increases the manufacturing cost. In view of the foregoing, such actuator has not been put to practical use until now.